The present invention relates generally to power control systems, to wireless control of electric power transfer switches, and more particularly, to designs of secondary transfer switches that allow a generator or other secondary power source to supply power to certain loads in order to reduce the electric power drawn from a primary source of power such as the utility grid.
The use of generators for backup power in the event of loss of utility grid power has been broadly accepted for decades. In recent years, the reciprocating engine-driven generators have been complemented by gas turbine engines, solar collectors, uninterruptible power system (UPS) devices and fuel cells as secondary sources of power. In typical applications, certain electric circuits that power critical equipment such as computer networks, emergency lighting, fire equipment, and the like have been xe2x80x9cbacked upxe2x80x9d by the standby or emergency power sources. In general, a user of standby power buys a standby system that is powerful enough to supply power for the critical loads mentioned, but not large enough to power an entire building or business. The size of the standby power source chosen is generally a financial decision, weighing the cost of the equipment against the probability of financial loss caused by a power outage, and the likelihood of such outage. In general, such machines are not marketed with the intent of their being used for primary power production. While a certain percentage of generators are used to provide power back onto the utility grid, this process is relatively rare and requires very expensive control equipment, generally called switch gear.
The typical emergency standby power generator is used to provide power to the critical loads within a building, on the consumer side of the utility meter, through a device known as an automatic transfer switch (ATS). The automatic transfer switch operates so as to connect the critical loads to the utility grid power when such power is present and available, but it senses the loss of utility power (outage) and provides a signal to start up the standby generator. When the generator has achieved the specified stable voltage and frequency, the transfer switch automatically disconnects the critical loads from the utility power source and reconnects them to the generator power. At such time as utility power becomes available, the automatic transfer switch reconnects the critical loads to the utility source. There is a wide range of sizes and features among transfer switches, but virtually all standby power generator connections follow the basic concept outlined above.
In the United States, there are at least 500,000 standby power generators in place, averaging about 100,000 watts of standby power each. This represents 50 Billion watts of available power sitting idle 99% of the time. This amount of power is as large as even the largest utilities, and could, if put into production, provide a significant solution to peak power shortages that utilities are experiencing. Unfortunately the current concept of providing standby power to critical loads is in conflict with the concept of using the machines for load reduction by transferring generator power to non-critical loads such as lighting and air conditioning which represent a good target for load reduction programs, either internally financially motivated, voluntary or utility mandated. It is considered unwise to power the critical loads by generator, and thus the current standby power paradigm does not support ready application of standby power in the load reduction application.
It is therefore an objective of the present invention to provide for methods and apparatus for making existing standby power available for use in load reduction programs to assist utilities in avoiding power shortages and resultant blackouts and to reduce consumer power costs during peak demand times.
To accomplish the above and other objectives, the present invention provides for methods and apparatus that are operative to couple standby power to certain non-critical loads that implement load reduction to assist utilities in avoiding power shortages and resultant blackouts. In implementing the present invention, a secondary transfer switch, referred to as a load reduction transfer switch (LRTS), is connected between a standby or secondary power source or generator and selected non-critical loads that may be safely powered by the secondary power source or generator.
An exemplary utility electrical distribution system comprises a primary utility source coupled to an electrical breaker panel that distributes power to a plurality of loads comprising non-critical loads, critical loads, and load reduction loads. A secondary power source is coupled to an automatic transfer switch that distributes power to the critical loads from the secondary power source if power is not available from the primary utility source. A load reduction transfer switch, wired in parallel to the automatic transfer switch, distributes power to the load reduction loads to reduce power demand on the primary utility source so long as the primary source is available.
An exemplary method that implements load reduction is used in a system that supplies power from a primary power source on a power grid to multiple sets of loads. The exemplary method comprises the following steps. A first transfer switch is coupled between one or more secondary power sources and one or more corresponding subsets of critical loads. Each first transfer switch is remotely controlled to supply power from the associated secondary power source to the corresponding subset of critical loads if power from the primary power source is unavailable. A remotely controllable load reduction transfer switch is coupled between each secondary power source and a subset of load reduction loads that are to be removed from the power grid during times requiring load reduction. Each load reduction transfer switch is remotely controlled to supply power from the secondary power source to its corresponding subset of load reduction loads in lieu of supplying power from the primary power source only when power from the primary power source is available and during times requiring load reduction.
The load reduction transfer switch may be installed in the same housing as a conventionally-used automatic transfer switch in new equipment production. However, in retrofit applications, a separate secondary load reduction transfer switch represents a simpler solution. In both cases, the load reduction transfer switch and the automatic transfer switch are connected in parallel to a utility power source, and the generator, or other secondary power source, and they both provide the switched power to appropriate loads; critical loads are connected to the automatic transfer switch and non-critical load reduction loads are connected to the load reduction transfer switch.
In general, the transfer switches are wired, however, so that the load reduction transfer switch and automatic transfer switch cannot both connect their loads to the secondary generator simultaneously, unless the secondary generator is sized for this application. In general, the load reduction transfer switch only operates when utility power is present and available, and the automatic transfer switch only operates when the utility power is absent. This logic is consistent with the design of the secondary generator, the transfer switches, and the chosen loads.
A wireless connection to the load reduction transfer switch may be used to provide a logical command to the load reduction transfer switch to initiate generator operation and to transfer power to the load when the generator has achieved stable operation. The application of the logic signal may be logically ANDed with a logic signal representing xe2x80x9cutility grid power availablexe2x80x9d. Thus, if the command is received and grid power is present, the command to the load reduction transfer switch would be applied. If the command is received and no grid power is available, then the load reduction transfer switch is not commanded into operation, because the generator may be in operation supporting critical loads, and the critical loads carry priority over load reduction requirements. At the end of the load reduction process, the transfer command logic signal is removed from the load reduction transfer switch, generator power is disconnected from the load reduction loads, and utility power is restored to these loads.
Prior to executing the transfer of loads to the generator, the control logic may provide a logic signal that xe2x80x9cnotifiesxe2x80x9d the loads of an upcoming power disturbance during the transfer process. For example, if the load is an air conditioning system, the control logic may open a relay in the thermostat circuit, allowing air conditioning blowers and pumps to come to a halt under their standard timing. This avoids the likelihood of inducing power spikes into the equipment during the transfer process. These power quality problems at transfer time, especially in xe2x80x9copen transitionxe2x80x9d transfer switches represent one of the primary impediments to the use of standby power generators in load reduction programs. That is, the potential for financial loss due to equipment damage by power surges may seem to be a greater risk than the value of the savings in power costs associated with the load reduction program incentives. Thus, the ability to xe2x80x9cpower downxe2x80x9d loads prior to transfer is an important aspect of the present invention.
The present invention is described in the context of wireless connectivity, although wired connection may readily be implemented. The preference for wireless connections comes from the ability to command large numbers of remote machines simultaneously via wireless communication, while achieving this function with telephone line connections is difficult, slow, and expensive. Further, the ability to install the load reduction transfer switch on existing generators without having to coordinate with local telephone providers is a major advantage of wireless connectivity. In order to match the wireless methods and capabilities in the area of broadcast control of multiple machines, a wire line connection would typically have to be configured into a computer network connection, and this further adds to cost and complexity.
Also, the controller may optionally measure the local load at the location of the electrical breaker panel, and automatically transfer load to the secondary generator via the load reduction transfer switch if customer demand approaches a threshold that would adversely affect the electricity bill. Industrial customer rates are commonly set by their peak demand, and this is why utilities monitor them on a 15 minute interval. The present invention thus may be used to minimize usage of the utility service in order to minimize electricity bills. Thus, the present invention not only provides for wired and wireless control of load switching, but also provides for automatic transfer of power to the secondary generator if customer demand approaches a threshold that would increase a customer""s bill. To implement this, the logic in the controller includes a customer demand threshold, that, when reached, causes the controller to switch the load reduction loads to the secondary generator.
Furthermore, the present invention not only provides for wired and wireless control of load switching, but also provides for automatic transfer of power to the secondary generator if customer demand approaches a threshold that would increase a customer""s bill. Multiple-pole load reduction transfer switches and associated control circuit may be employed to know or sense the difference between power-out and peak power reduction needs, and automatically connect the proper load to the secondary power source. The use of multiple-pole load reduction transfer switches addresses local measurement of power and automatic switching to reduce the need for utility power during high customer demand situations.